The plants are deciduous or evergreen perennials (rarely shrubs) with a rhizome or corm (rarely a bulb in some New World and Eurasian species).

The leaves are usually two-ranked with the blade oriented vertically to the stem and thus sheathing it at the base. This results in the characteristic fan-like arrangement found in genera like Iris. This type of leaf lacks distinct upper and lower leaf surfaces. In many South African species the leaf has a thickened midrib and often variously thickened or winged margins that may also be crisped. In some species the leaves are needle-like with narrow longitudinal grooves. Species of Moraea are unusual in the family in having channelled leaves with a distinct upper and lower surface.

The flowers are arranged in various ways, either in small clusters between large bracts, or in a spike (rarely solitary), with each flower held between two small or large bracts. The flowers are radially or bilaterally symmetrical with six tepals (petals). These may be similar to one another or different, usually with the upper larger. They are usually brightly coloured, sometimes with contrasting spots and stripes, and may be very fragrant. The petals are either separate or joined at the bottom into a short or long tube. The flowers of many Iridoideae, such as all Aristea species, last less than a single day, but in most species they last for three or four days.

The three stamens are inserted at the base of the petals or just within the tube (if present), opposite the outer three tepals. They are either symmetrically clustered in the centre of the flower when this is radially symmetrical, or arched together under the upper tepal or onto the lower tepal in bilaterally symmetrical flowers. In some species of Moraea the stamen filaments are joined into a tube.

The ovary is inferior (superior in the Tasmanian Isophysis) with three locules each containing several to many ovules attached to the centre. Each flower has a single style that usually has three branches near the tip, each of these sometimes forked as well. In some genera (Dietes, Ferraria and most species of Moraea), the style branches are flattened and petal-like.

The fruit is a dry capsule that usually splits open along three sides to release the seeds. These are very variable in shape. In most genera they are tetrahedral or variously angled and without obvious adaptations for dispersal. Winged seeds adapted to wind dispersal characterise Gladiolus and Tritoniopsis, and also occur in some species of Hesperantha. Globular seeds with shiny coats that are relatively long-lived occur in several genera of Ixioideae. Chasmanthe aethiopica has fleshy seeds adapted to dispersal by birds, and several other species that grow in more wooded places, like Chasmanthe and some freesias, have reddish or black seeds that mimic fleshy seeds.